Laser lithotripsy

ABSTRACT

A laser lithotriptor includes a laser adapted to emit pulsed light which is absorbed by water in the vicinity of a human stone or concrement to cause rapid erosion of the stone. A light transmitting device such as a fibreoptic cable is employed inside of an endoscope to direct the laser pulses to the vicinity of the stones. An irrigation apparatus also ensures that the tip of the light transmitting device and the stone are continuously immersed in water and also serves to remove the powder-like debris of the disintegrated stone from the body. Preferably, a NdYAG laser operating at 1.44 μm which emits 27 pulses per second is coupled to the body stone through an anhydrous quartz fibreoptic cable passing through the interior of an endoscope.

This is a division of co-pending application Ser. No. 07/506,446 filedApr. 6, 1990.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to laser destruction of human calculi.

Lithotripsy, the crushing of human stones into easily removablefragments, is an old enterprise. Frere Jacques (of the French Folk song)was an itinerant lithotomist 300 years ago.

Modern medical practitioners, until recently, viewed gall bladder,kidney and ureteral stones as being removeable only by open surgery.Bladder stones, however, have been treated by endoscopic lithotripsy formany years. Physicians view the interior of the bladder with acystoscope. This device is passed via the urethra into the bladder. Anelongated lens combined with an eyepiece is passed along and attached toa sheath so that an image of the interior of the bladder may be seen.Typically, a cystoscope contains a means for passing irrigating fluidinto and out of the bladder, a means for removing tissue samples fromthe bladder and a means of visualization.

Various methods of crushing bladder stones have been combined with thecystoscope: for example, mechanical crushing, mechanical drilling andmore recently, ultrasonic disintegration.

The first ultrasonic lithotripsy of bladder stones occurred in Germanyin 1968. The combined means of a cystoscope, a piezo-electric ultrasonictransducer and an interchangable ultrasonic probe was used. The probe ispassed into the bladder under visual control. It will disintegrate somebladder stones on contact. Ultrasonic lithotriptors will not break hardstones. Each probe may be used for approximately 100 pulses before itmust be replaced. Ultrasonic lithotriptors are consequently limited inuse and expensive to operate.

The interior of the kidney (known as the pelvis of the kidney) may bevisualized with the nephroscope, which is similar in use and appearanceto the cystoscope. This endoscope is said to be used percutaneouslywhere the sheath is passed into the kidney through the abdominal wall.Since the nephroscope became available, ultrasonic lithotripsy of kidneystones has become common practice. This practice is described, forexample, by J. E. Lingeman in his article "Current concepts on therelative efficacy of percutaneous nephrostolithotomy and extracorporealshockwave lithotripsy" in World Journal of Urology 5, 229, 1987, and byG. E. Brannen, W. H. Bush, R. E. Correa, R. P. Gibbons, and J. S. Elderin their article "Kidney Stone Removal, percutaneous versus surgicallithotomy" in Journal of Urology, 133, 6, 1985.

Approximately 50% of symptomatic urinary stone disease results fromstones in the ureter. Ureteroscopes which may be either rigid orflexible are typically longer and thinner than other endoscopes.Ultrasonic lithotripsy is used very little in the ureter because of therigid nature and relatively large diameter of the ultrasonic probe. Seefor example the article by J. L. Huffman, D. H. Bagley, H. W.Schoednberg and E. S. Lyon, "Transurethral removal of large ureteral andpelvic calculi using ureteroscopic ultrasonic lithotripsy" in theJournal of Urology, 130, 31, 1983.

Endoscopic destruction of gall stones has not become common medicalpractice although it is clearly possible.

The introduction in the early 1980's of the so called extracorporealshockwave lithotriptor (E.S.W.L.) resulted in a significant improvementin the treatment of kidney stones. In this type of device a shock waveis created by an underwater high current spark discharge. By means of anelliptical acoustic reflector this shock wave is focused through thesoft abdominal wall and kidney onto the kidney stone. The shock wave haslittle damaging effect on soft tissue but fractures hard stones. Theresulting crushed stone is passed through the urinary tract. TheE.S.W.L. is described, for example, by C. Chaussy, E. Schmiedt, D.Jocham, W. Brendel, B. Forsmann and V. Waltham in their article "Firstclinical experience with extracorporeally induced destruction of kidneystones by shock waves" in the Journal of Urology 127, 417, 1982 and morerecently by G. W. Drach in "Report of the United States CooperativeStudy of Extracoporeal shock wave lithotripsy, in the Journal ofUrology, 135, 1127, 1986.

The E.S.W.L. is less effective for the treatment of ureteral stones.This is partly because of the difficulties in avoiding the pelvis andpartly because ureteral stones are not immersed in liquid so that shockwave coupling to the stone is less efficient. For a discussion of thislimitation of E.S.W.L. see the article by J. Graff, J. Pastor, P. Mach,W. Michel, P. J. Funhe, and T. Senge, "Extra corporeal shock waveTreatment of Ureteral Stones" in the Journal of Urology, 137, 143A,1987.

The laser has recently been used as an alternative means for thedestruction of ureteral stones. An extensive review is provided by thebook entitled "Laser Lithotripsy" edited by R. Steiner, Springer Verlag,1988. Typically the laser is focused into a fibre optic which is passedalong a rigid or flexible ureteroscope. The ureteroscope is insertedthrough the bladder into the ureter and the stone is visualized. Theoperator may in this way direct intense pulses of light onto or in thevicinity of the stone and thus cause fracturing and disintegration ofthe stone. In the current state of the art as described by Steiner in"Laser Lithotripsy", two laser sources are effective in lithotripsy: thepulsed dye laser and the Q-switched NdYAG laser.

For a description of the operation of the pulsed dye laser, see thearticle by G. M. Watson, S. Murray, S. P. Dretley and J. A. Parrish inthe Journal of Urology, 138, 195, 1987. Typically, pulses of visiblelight in the spectral region from 445 to 577 nm and of duration of 1 μsto 300 μs are used. The energy of each pulse is typically 10 mJ to 60mJ. Typically the distal laser fibre tip touches the surface of a humanstone which is immersed in water. A light pulse of sufficient intensityis then passed along the fibre. When a threshold of energy is exceeded abrilliant flash of light is emitted by the stone. This flash isaccompanied by the disintegration of part of the stone. The white flashis accompanied by a clicking sound. The light emission by the stone andthe shock which fractures the stone are attributed to the formation of alaser induced plasma. A discussion of this mechanism is in the paper byG. M. Watson.

Although the dye laser is reported to fragment all human calculi but thevery hard uric acid and calcium oxalate monohydrate stones, it hasseveral clinical shortcomings. The fragments of stone produced by dyelaser lithotripsy tend to be relatively large compared with the powderproduced by externally applied shock waves. Extraction of debrisfollowing lithotripsy is consequently a problem. If sharp debris isimpacted in the ureter, for example, this represents a significantclinical problem.

Another difficulty encountered by users of dye laser lithotriptor is thevariability of effectiveness. Formation of a plasma in a laserirradiated stone results from absorption of light by pigments in thestone. Pigmentation is variable. In renal stones it varies from almostwhite to dark brown. The laser conditions needed for formation of aplasma are difficulty to predict because the color of the stone is notknown prior to lithotripsy. The size of fragments created by the dyelaser is typically larger than fragments produced by a shock wave. Thesize of dye laser-produced fragments increases as the laser energyincreases. Fragment size also increases as the depth of lightpenetration into the stone increases. Extraction of large fragments ofstone from a ureter following dye laser lithotripsy is a significantclinical problem.

In an attempt to find a laser lithotriptor which does not depend uponthe photochemical properties of human concrements, several groups havedeveloped Q-switched NdYAG laser lithotriptors. See, for example, thearticle by F. Wondrazek and F. Frank, "Devices for intracorporal Laserinduced Shock Wave Lithotripsy" in Laser Lithotripsy, Springer Verlag,1988. Typically, in this type of device a 10 ns laser pulse from aQ-switched NdYAG laser with the wavelength of 1.06 μm is transmittedthrough a fibre from the laser to the vicinity of a stone. The stone isimmersed in irrigating liquid which is typically water on saline andessentially transparent to the 1.06 μm laser light. Consequently, lightemerging from the fibre will pass freely through the liquid and strikethe stone or tissue in the vicinity of the stone and be absorbed. In themethod of Q-switch NdYAG laser lithotripsy a small lens is attached tothe output or distal end of the fibre so that light emerging from thefibre is focused a few millimeters from the said lens. If the intensityof laser light is sufficiently high a small plasma will form at thefocus in a manner which is known as laser breakdown. The plasma absorbslight emerging from the fibre so that little light strikes the stone ortissue. The absorption results in a rapid deposition of energy into asmall volume of plasma. The expansion of the hot plasma gases is limitedby the surrounding liquid and an explosive increase in pressure results.The resulting shock wave radiates from the plasma in all directions atthe speed of sound in the liquid. In the method of Q-switched laserlithotripsy a small parabolic reflecting surface is attached to thedistal end of the fibre so as to reflect part of this shock wave towarda stone placed typically 3 mm from the plasma. Repeated impact of theseshock waves on a stone tends to disintegrate the stone so that alithotripic effect results. This method has the advantage that thephotochemical composition of the stone does not influence thelithotripsy and the resulting stone fragments are similar to thoseproduced by E.S.W.L. The disadvantages of this method are: the lensholding chamber is typically larger than two millimeters in diameter sothat access to stones through a ureteroscope is limited; the largerrigid ureteroscope must be used; and the exposure of the lens to theplasma shock wave will destroy the lens after approximately 100 pulses.The limitations of this type of lithotripsy are discussed by S. Thomas,J. Pensel, W. Meyer and F. Wondrazeh in "The Development of anEndoscopically Applicable Optomechanical Coupler for Laser Induced ShockWave Lithotripsy" in Laser Lithotripsy, Ed. R. Steiner, Springer Verlag,1988.

In the present invention a method of laser lithotripsy uses laser lightwhich is absorbed by water. Pulses of light absorbed by water in thevicinity of the stone cause erosion of the stone.

The geometry of the present laser lithotriptor includes a pulsedNeodymium Yttrium Aluminum Garnet, (NdYAG) laser operating at thewavelength 1.44 μm. This laser is described in the patent applicationnumber U.S. Ser. No. 06/933,10 filed by John Tulip in 1986. Unlike otheremissions from the NdYAG laser, for example at the wavelengths of 1.06μm and 1.32 μm, NdYAG laser emission at 1.44 μm is strongly absorbed bywater. The depth over which this laser light is essentially absorbed bywater is approximately 0.3 mm. Absorption of laser energy by waterresults in water heating and even vaporization if the laser light issufficiently intense. In one example, this effect is used to vaporizehuman body tissue water with a focussed NdYAG 1.44 μm laser beam forsurgical purposes. If the NdYAG laser is flashed or pulsed, theradiation may appear in intense, short bursts or pulses of energy. Suchpulses of 1.44 μm radiation quickly heat and vaporize water.

Another part of this laser lithotriptor system is a quartz fibreoptic.Pulses of light from the said 1.44 μm NdYAG laser may be focussed intoand along quartz fibreoptic. In particular quartz fibreoptic with verylow OH content, commonly known as anhydrous quartz fibreoptic,effectively transmits 1.44 μm light. This fibreoptic may be used todirec laser pulses to the vicinity of body stones by passing thefibreoptic along such endoscopes as the ureteroscope.

Another part of this laser lithotriptor geometry is water in thevicinity and in contact with body stone. It is common practice toirrigate the bladder, ureter or kidney with water or water solutionssuch as saline during endoscopic examination. Natural body fluids arealso composed largely of water. Therefore body stones are normallyimmersed in water.

We have discovered that a combination of these three means, appliedcorrectly, will rapidly erode even the hardest calcium oxalate bodystones.

It has been discovered that a microscopic explosion may occur at thedistal, or output, tip of the fibreoptic when the fibre tip of thefibreoptic is placed in water and a pulse of 1.44 mm radiation istransmitted through the fibre. Apparently no plasma occurs in thisexplosion, no visible emission can be seen and no lens is placed at thefibre tip. The laser pulse period is typically up to tens ofmilliseconds which is much longer than the 10 nanosecond pulse period ofthe Q-switched 1.06 mm NdYAG laser. The velocity of sound in water issufficiently high that a shockwave created by a millisecond long laserabsorption induced micro explosion would travel away from the fibre tipin a time which is much less than the laser pulse period. Unlike theQ-switched NdYAG 1.06 μm laser, the 1.44 μm laser is absorbed by water.Absorption by water causes a micro-explosion.

1.06 mm radiation is absorbed very weakly by water so that plasmaformation at the fibre tip is necessary to cause a micro explosion. With1.44 μm radiation rapid heating and vaporization of water in thevicinity of the fibre tip causes a rapidly expanding vapour bubble. Theexpansion of this bubble is inhibited by the fibre tip and thesurrounding water so that a miniature laser absorption-induced explosionoccurs. This explosion is accompanied by a sharp audible click. Theselaser absorption induced micro explosions have been examined using highspeed shadow photography which reveal the shape and velocity of theexpansion front of the explosion. These images show a sharp,well-defined front which is similar in appearance to the domed explosionfront commonly photographed during nuclear explosions.

In one example, a distal fibre tip was cleaved flat and perpendicular tothe fibre axis. Shadow photography did not show a spherically shapedexpansion as might be expected, but a highly directional expansion awayfrom the tip in the direction of the fibre axis. The expansion velocitywas initially typically 2 millimeters per millisecond and resulted in abubble typically 5 mm in length and 2 mm in diameter.

In another example a fibre was drawn to a point by heating the fibrewith a flame and pulling two parts of the fibre apart. This pointedfibre tip produced very different shadow photographs. A sphericalexpansion occurred close to the tip of the fibre point and resulted inan approximately spherical bubble of about two to three millimetersdiameter.

Continued pulsing of a fiber tip for many thousands of pulses does notapparently influence the formation of absorption induced microexplosions in water. Unlike the Q-switched 1.06 μm NdYAG laserlithotriptor, damage to the fiber tip surface (which occurs with use andwhich appears similar to a sand blasting effect) does not influence thecreation of micro-explosions in water since the formation ofmicro-explosions using 1.44 μm radiation does not rely upon the use of afocusing lens.

It has been discovered that micro-explosions, in water at the tip of afiberoptic and created by pulsed 1.44 μm radiation, will erode humanstones. If a human stone is immersed in water and the said laseractivated fiber tip is brought in contact or near the stone, rapiderosion of the stone surface will occur and fine, powdery, debris willappear in the water. This debris rapidly obscures the stone from view.In contrast, if the stone is placed in air and the said laser activatedfiber it is brought near the stone, melting of the stone surface occursand no erosion is observed. The presence of water around the stone is anecessary means for laser erosion to occur.

If the 1.44 μm laser-activated fiber tip touches the surface of thestone when high average laser power is applied, a bright flash(associated with plasma formation) may occur. Melting of the fiber tip,melting of the stone and adhesion of the fiber tip to the stonefrequently accompany flashing. This undesirable plasma formation isunlike the dye laser lithotriptor (which requires the fiber to touch thestone and cause a flash in order to fragment the stone.) Despiteflashing and melting by touching the stone with the fiber tip, it ispossible to push the fiber several centimeters through even very hardstone. This is achieved by repeatedly removing the fiber from the smallcylindrical hole created by pushing the fiber optic into the stone inorder to permit water to enter the hole.

Experiments have been undertaken to find the best distance between thestone surface and the activated fiber tip. In one, fiber was passedthrough a channel in a cystoscope so that the tip was visible throughthe lens of the cystoscope--a stone and the fiber tip could be observedsimultaneously under water in a rigid container. Small pieces of chalk,(a widely-accepted substitute for soft human calculus,) of known sizewere fixed by epoxy to the base of the water container. A small wire wasattached to the cystoscope to control the distance between the fiber andthe chalk. The time required to totally erode a chalk sample wasmeasured as the distance to the chalk was varied. The fiber tip wasmoved manually across the chalk in a circular pattern which resulted incircular grooves which progressively eroded the chalk. The time requiredto destroy the chalk sample was used as a measure of erosion rate. Boththe pointed and flat fiber tips eroded the chalk most effectively withtheir tips within two millimeters of the sample. Little improvement inerosion rate resulted from placing the fiber tip closer than 2millimeters. When the laser was used at low average laser power the besterosion rate occurred when the fiber tip was in contact or close tocontact with the stone. The pointed fiber tip generally produced afaster erosion rate than the flat fiber tip. Examination of theinteraction of the micro-explosions and a stone was performed withshadow photography. The explosion expansion front from a flat fiber tipstrikes the stone surface and tends to be deflected laterally andperpendicular to the direction of the fiber axis. The explosionexpansion front from a pointed fiber strikes the stones and tends to bedeflected away from the stone along the axis of the fiber. For thisreason a greater momentum change of the expansion occurs for a pointedfiber tip which may explain the greater stone erosion rate which resultsfrom use of a pointed fiber tip.

Light at 1.44 μm is absorbed by water within 0.5 mm. Q-switch 1.06 μmwavelength light from the NdYAG laser and 0.53 μm wavelength light fromthe dye laser pass through water essentially unabsorbed. If thedirection of the fiberoptic tip is deflected so that light does notstrike the stone, the light can pass freely through the surroundingwater and strike tissue. In order to avoid accidental injury, theaverage power from both of these laser lithotriptors is limited to a fewwatts. This results in slow stone destruction rates for both theQ-switch NdYAG laser lithotriptor and the dye laser lithotriptor.

In order to assess the safety of 1.44 μm laser lithotripsy, animalexperiments were performed. Exposed skin on an anesthetized small animalflank was submerged in water and exposed to the activated fiber tip. Inthe example of a flat fiber tip, tissue injury was observed only whenthe axis of the fiber was perpendicular to the skin surface. When thefiber was parallel and in contact with the skin, no injury wasobservable for an average laser power of 45 watts emerging from thefiber. When the fiber was perpendicular to the skin, injury was observedwhen the fiber tip was less than 3 mm from the skin with an averagelaser power of 45 watts. In the example of pointed fiber tip, injury wasobserved only when the fiber tip was within 1 mm of the skin with anaverage power of 45 watts. Consequently, for the pointed fiber tip it isnecessary to essentially touch tissue to cause accidental injury.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated forcarrying out the invention.

FIG. 1 is a schematic view illustrating the laser lithotriptorconstructed and used in accordance with the principles of the presentinvention.

FIG. 2 illustrates the juxtaposition of the fiber tip and the stone.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 illustrates the laser lithotriptorconstructed and used in accordance with this invention. Laser, 1, isadapted to emit radiation which is absorbed by water or water solutions.Although not to limit the generality of the invention, this may be, forexample, the CO₂ laser operating at the wavelength 10.6 μm, the NdYAGlaser operating at 1.44 μm, the ErYAG laser operating at 2.9 μm, theT_(m) H_(o) C_(r) YAG laser operating at 2.16 μm, the HF laser operatingat 2.9 μm or the C_(o) M_(g) F₂ laser operating at 1.9 μm. As a specificexample, the laser 1 may be an NdYAG laser adapted to emit radiation at1.44 μm and to emit light pulses with energy adjustable from zero to 2Joules, pulse width adjustable from 0.1 to 100 milliseconds, pulserepetition rate adjustable from 0 to 100 pulses per second and averagelaser power emission adjustable from 0 to 50 watts.

Pulsed pumping source 2 drives the laser 1 so as to produce repetitivepulses of light from the laser. For examples, this may be the electricalexcitation means for the lamps of the NdYAG laser or it may be theelectrical excitation means for the CO₂ laser discharge. Other means ofpulsing the laser are anticipated. For example, an electrical ormechanical shutter within the laser resonator will result in pulsedlaser emission known in the art as Q-switching. As a specific example,pumping source 2 may be a switched current source which drives the laserpumping lamps of an NdYAG laser adapted to operate at 1.44 μm. The pulseduration varies from nearly zero to 100 milliseconds and the pulserepetition rate varies from one 1 to 100 pulses per second.

Light delivery means 3 transmits the laser light from the laser into thehuman body to the proximity of a stone. The delivery means may be afiberoptic, it may be a rigid light guide or it may be a flexible lightwaveguide. As a specific example, this may be a 600 μm quartz corefiberoptic manufactured to have low water content. This is known in theart as anhydrous quartz fiberoptic.

The body part, 4, illustrated is the ureter. This may be the bladder theurethera, the cervix of the kidney, the gall bladder or the common bileduct. This is not to limit the generality of the invention sincecalcification occurs in other body parts such as blood vessels.

Irrigation means, 5 carries water or a water solution to the vicinity ofthe stone. This means of ensuring that the fiber tip and the stone areimmersed in water also serves to remove the powder-like debris from thebody. It may be plastic or metal tubing or it may be liquid-conductingchannels in a rigid or a flexible endoscope. As a specific example,irrigation means 5 may be the irrigation channel of a resectoscope whichhas been modified to pass a fiberoptic.

Referring now to FIG. 2, this illustrates the juxtaposition of the laserfiberoptic and the human stone.

The fiber tip, 6, may be the flat end of a fiberoptic or it may be thepointed or rounded tip of a fiberoptic. It may also be the output windowfor a hollow light guide or a flexible waveguide. It may also be thepointed or flat attachement made for a transparent hard material such assapphire.

The stone, 7, may be any form of human concrement such as softcholesterol gall stone or hard calcium oxalate urinary stones. Thestone, 7, is disposed closely to the fiber tip, 6, for maximumlithotriptic effect.

As a specific example the distance, 8, between the stone and fiber tipis 2 mm. The immersing liquid, 9, covers the fiber tip and the stone andin particular fills the space, 8, between them. This liquid should belight-absorbing. It may be water or a water containing solution or itmay be a light-absorbing solution.

When used as a lithotriptor the preferred geometry is NdYAG laseroperating at 1.44 μm which emits 27 pulses per second with a pulseenergy of 1.5 Joules. This laser is coupled to the stone through a 600μm core anhydrous quartz fiberoptic. The fiber tip is held within 2 mmof the stone surface and is pointed. Both the fiber tip and the stoneare immersed and irrigated with water.

Various modes of carrying out the invention are contemplated.

I claim:
 1. A method of destroying a concrement in the human body, themethod comprising:supplying a liquid to the vicinity of a concrementlocated in a human body, the liquid being capable of absorbing laserlight having a chosen frequency; placing one tip end of a lighttransmission means closely adjacent and directed towards the concrement,whereby a gap is left between the tip end of the light transmissionmeans and the concrement, the liquid filling the gap; and applying tothe light transmission means laser light pulses having the chosenfrequency to create laser absorption induced micro-explosions in theliquid, whereby the concrement is eroded and produces debris.
 2. Themethod of claim 1 further including removing the liquid and the debrisfrom the vicinity of the stone.
 3. The method of claim 2 in which thetip end of the light transmission means is placed within 2 mm of theconcrement.
 4. The method of claim 2 in which the liquid contains water,and the frequency is a frequency that is absorbable by water.
 5. Themethod of claim 4 in which the laser light is generated by a 1.44 μmNdYAG laser.